ARM: 6209/3: at91_udc: Add vbus polarity and polling mode

Allow the vbus signal to optionally use polling. This is required if
the vbus signal is connected to an non-interrupting io expander for
example. If vbus is in polling mode, then it is assumed that the vbus
gpio may sleep. Also add an option to have vbus be an active low
signal. Both options are set in the platform data for the device.

Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>